Dispersive charge sensing of quantum dots in Ge/Si core/shell nanowires*

Holes in Germanium/Silicon core/shell nanowires are a powerful platform to study and optimize the properties of spin qubits. This is a consequence of the strong, gate-tunable direct Rashba spin-orbit interaction, which arises from the strong 1D confinement in the nanowire. In turn, this enables toggling a spin qubit between an ultrafast control mode with Rabi frequency above 400 MHz and an idling mode with weaker SOI and longer coherence times (Froning et al. Nat. Nano. 16, 308-312 (2021)). So far, experiments in this system have been done in DC transport, making it hard to measure more than two quantum dots in series and preventing single-shot readout.

Here, we present fast, gate-dispersive charge sensing measurements in a Ge/Si nanowire device with a tank circuit situated on the sample PCB. A Strontium Titanate (STO) ring-varactor, made in house, is employed to in-situ tune the tank circuit to the perfect impedance matching at temperatures down to 10 mK. Using this technique, we can sense the depletion of the nanowire to the few-hole regime and present progress towards establishing fast single-shot spin readout.